Technical Field
The present disclosure relates to a power supply apparatus and a power supply method.
Background Art
There are many large-sized vehicles such as trucks or buses that have two power supplies a 24V-power supply that mainly drives a starter motor and a 12V-power supply that drives in-vehicle accessories. As a method of supplying power from the two power supplies, it is common to connect 12V-secondary batteries in series, and to obtain 24V as their total voltage and obtain 12V from one of the secondary batteries.
As has been described above, when the two secondary batteries are connected in series in the aforementioned manner, there may be a case in which the discharging of a secondary battery on a 12V-side progresses faster as compared to the other secondary battery, and a difference in the charging rate may occur between the two secondary batteries. In such a case, the life of one of the secondary batteries may shorten, or as the discharging progresses, it may not be able to drive the starter motor.
Accordingly, in order to prevent such a situation, in the related art, there are a technique of connecting a resistance element to a secondary battery on a high-voltage side and discharging electricity to balance them (Japanese Laid-Open Patent Publication No. 2007-267454), a technique of transferring an electric power from a secondary battery of a high voltage to a secondary battery of a low voltage using a convertor or a transformer (Japanese Laid-Open Patent Publication Nos. 2010-93980 and 2000-60019), and a technique of equalizing a charged state by bypassing a secondary battery that has come to a full-charge state during the charging (Japanese Laid-Open Patent Publication No. 1998-14002).
According to the technique described in Japanese Laid-Open Patent Publication No. 2007-267454, since an electric power is converted into heat by a resistor, there is a disadvantage that efficiency is low due to an occurrence of a loss of an electric power. According to the technique described in Japanese Laid-Open Patent Publication No. 2010-93980, since an electric power is transferred between the secondary batteries, there is a disadvantage that time is required for the transfer. According to the technique described in Japanese Laid-Open Patent Publication No. 2000-60019, since an electric power is transferred using a transformer, there is a disadvantage that the transfer is not appropriately performed due to a winding ratio of the coil and that time is required for the transfer. Further, according to the technique described in Japanese Laid-Open Patent Publication No. 1998-14002, since it is a technique of managing the charging, there is a disadvantage that the discharging cannot be managed.